Missing or Incomplete Sequence of Operation

MTN recently had an opportunity to help a construction manager troubleshoot an underperforming air handler that had been installed six months before. The design was complete, the construction was complete, and the Owner was complete......ly unhappy (see what I did there). No one wants an unhappy Owner; seriously no one, maybe lawyers, but no one else. The design engineer hasn't looked at the project in months, possibly years. The construction team has been off the project for months but here comes summer, and the building is hot.

MTN started our review with the design drawings, trying to learn how the design engineer intended for the chiller, air handler and downstream terminal equipment to work together to achieve thermal comfort. There were control diagrams for the chiller and terminal units, but the air handler sequence was nowhere to be found.

When sequences are missing or incomplete, it almost always causes the design intent to not be achieved. Some mechanical engineers look to a controls contractor to provide a sequence of operation, controls diagrams and controls specifications for their project's mechanical equipment. There are many controls contractors who are happy to provide this service. However, most projects are open bids and therefore, the controls contractor who put all this free controls design into the project, may not win the project. They know this going in, so do you think they put their best effort into the design? Probably not. Even if they do, they cannot read the design engineer's mind, so they still may miss critical elements of the design intent.

When design engineers rely on controls contractors for their control designs, we often find equipment that is missing or incomplete. In the worst examples, the design intent is completely missed. This is especially apparent in critical spaces like Museums: A Beautiful Challenge (mtnengr.com). Where we often see the wrong setpoints used, missing dehumidification or building pressure sequences, among many other issues that lead to the Owner being unhappy with the final outcome and the entire project team trying to figure it out at the end of construction. Or, if a good commissioning provider is on the project, a slew of design review comments.

For design engineers who are currently not completing their own control designs, there are online resources out there that can help. Automated Logic Corporation (yes, a control's manufacturer), provides a great resource at CtrlSpecBuilder for control diagrams, sequences of operation, and control specifications. While there is some ALC language in there, it is freely editable and completely customizable.

Start doing your own controls design, your clients deserve it, and you'll hear a lot less 'whining' from the commissioning agents (like MTN) on your projects during design review.